Epoxy resins have been precatalyzed with phosphonium and other compounds to provide latent compositions which form advanced, higher molecular weight epoxy resins when admixed with an aromatic hydroxyl-containing compound as disclosed by Perry in U.S. Pat. No. 3,948,855 and Can. 893,191; by Dante et al. in U.S. Pat. No. 3,477,990; by Mueller et al. in U.S. Pat. No. 3,547,881; by Tyler, Jr. et al. in U.S. Pat. No. 4,366,295; and by Cragar in Can. 858,648.
While compositions containing these catalysts and an epoxy resin are somewhat stable, such compositions which also contain an aromatic hydroxy-containing compound are lacking in stability.
Curable compositions containing epoxy resins and aromatic hydroxyl-containing compounds and a catalyst therefor would be highly desirable in the preparation of storage stable coatings, storage stable electrical encapsulants, storage stable formulations for preparing mechanical and electrical laminates and composites, storage stable one package molding compositions, storage stable curable compositions for use in resin transfer molding (RTM) and reaction injection molding (RIM) applications and the like.
Copending applications Ser. No. 07/274,250 filed Nov. 18, 1988, Ser. No. 07/274,227 filed Nov. 18, 1988 and Ser. No. 07/274,264 filed Nov. 18, 1988 disclose catalysts which render a mixture of an epoxy resin and an aromatic hydroxyl-containing compound storage stable; however, these catalysts which are formed by contacting an imidazole compound or an onium compound or an adduct of an amine and an acid having a strong nucleophilic anion with an acid having a weak nucleophilic anion such as fluoboric acid result in compositions having a relatively long induction time at elevated curing temperatures.
It would be desirable to have available catalysts which render compositions containing epoxy resins and compounds containing phenolic hydroxyl groups storage stable at storage temperatures and which also result in curable compositions having reduced induction time at elevated curing temperatures.